This invention relates to medical resuscitated bags for ventilation during cardiopulmonary resuscitation and during patient transport and to cardiopulmonary resuscitation training systems.
The development of air trapping or auto-peep during patient ventilation with resuscitation bags operated by the hands of a nurse, respiratory therapist, or physician represents an important problem. A recent study published by the present inventors in Critical Care Medicine shows that severe air trapping is induced by these bags in patients with obstructive lung disease or asthma. This air trapping causes a rise in positive end expiratory pressure (PEEP) in the chest. The pressure in the chest becomes more and more positive preventing blood flow back to the heart, this can result in a fall in cardiac output which can result in shock and severe patient injury and death. This is especially important when associated with blood volume depletion as with trauma or sepsis. In such a case any increase in PEEP within the chest can potentially decrease the resuscitation potential of a patient.
This rise in pressure is often insidious and occurs in slow incremental amounts with each breath until a new steady state is reached with substantial mean alveolar pressure and PEEP levels about which the operator is entirely unaware. The failure to achieve adequate cardiac output in this situation is often attributed to other causes and may be perceived as a generic “pulseless electrical activity” (PEA) for which inappropriate and potentially dangerous cardiac stimulating pharmacological therapy may be urgently applied by ACLS protocol. Failure to correct this hidden pressure build up within the chest cavity during CPR can result in resuscitation failure and death. This is likely to be one of the reasons that the death rate is so high in asthma patients resuscitated by the standard ACLS protocols used throughout the U.S. by emergency rooms and paramedic squads. The ACLS protocol calls for the patient to be bagged at a rate of one breath for every five compressions, which we have shown experimentally, causes severe air trapping and potentially life-threatening PEEP in a large population of patients. One of the present inventors is aware of at least two patients who died as a result of this problem when other doctors and healthcare workers, unaware of the development of Auto-Peep, attempted to apply ACLS protocol to patients who had advanced obstructive lung disease.
For these reasons there has been a long and critical need for a resuscitation bag system and method which can warn the operator when the patient has trapped air or Auto-Peep so that the ventilation rate or volume can be reduced to allow time for the patient to completely exhale. This will allow the pressure to fall within the chest to lower levels allowing sufficient blood return to the heart. In addition there has been a long and critical need for a system and method for providing hands on training of the clinical findings and significance of hyperinflation during CPR.
It is considered important that any new medical resuscitated bag have a low manufacturing cost, as most resuscitation bags are now disposable. The present inventors recognized that it is important that all bags provide an indicator of trapped air both in the field and in the hospital. For this reason it is considered desirable to provide an embodiment of the indicator which is inexpensive and disposable, so that comprehensive implementation is easily achieved.
The present invention comprises a simple resuscitation bag system including a bag having a port for connection to an oxygen source, a conduit with a terminal for connection with an indwelling endotracheal tube, a one way valve intermediate the bag and the terminal to prevent exhalation back into the bag, an exhalation port, and an indicator connected with said system which indicates when pressure and/or airflow from the patient is present after the inhalation has been completed. The indicator allows the recognition of trapped air during bagging so that survival in patients with obstructive lung disease or low blood volume can be improved during CPR. The pressure or flow indicator can be adjacent the bag or adjacent the connecting tubing between the patient and is preferably mounted adjacent with or is integral with the exhalation port. The indicator can be a simple pressure or flow sensing device such as a disposable pneumotachometer or other type of flow and/or pressure sensor as are well known in the art. The indicator is sized and configured to provide automatic visual or auditory indication of persistent airflow or pressure during exhalation so that the exhalation does not need to be stopped or any changes made by the operator to identify the presence of persistent flow which can indicate air which will be trapped if the bag in manually compressed before the exhalation process in completed. In the preferred embodiment the indicator is a simple disposable elastomeric member which is mounted adjacent the exhalation conduit of a resuscitation bag or endotracheal tube and which is positioned so as to be readily visible to the operator and which deforms in the presence of flow and/or pressure such that the presence of said deformation can be used to indicate the persistence of flow and/or pressure during exhalation after a manual inflation of the lungs by the bag system.
In another preferred embodiment of the invention, the indicator consists of an auditory port located through the side of the exhalation port to which a listening device such as a disposable esophageal stethoscope is connected. The esophageal stethoscope is comprised of a long flexible tube with a standard fitting, such as a Luerlok fitting, at one end and an earpiece at the other end, a design well known in the art. The earpiece is placed in the ear of the operator/rescuer. Gas flow is detected by the sound of gas flowing through the exhalation port and into the ambient environment. A small protuberance is located on the interior wall of the exhalation port and in proximity to the auditory port to enhance the level of sound. In a further improvement to this embodiment, a whistle is mounted on the interior of the exhalation port and in proximity to the auditory port. The whistle generates a sound in the human auditory range of frequencies as gas flows through it. Gas flow is then detected, after a manual inflation of the lungs by the bag system, by the sound generated by the whistle.
One reason that air trapping is poorly recognized in the field is that advanced cardiac life support education does not teach well the physiologic issues and clinical findings relating to this important adverse process. For example PDA is described as caused by the “5 Hs”. However, the present inventor realized that a “6th H” (hyperinflation) should be included as one of them to teach paramedics, nurses, EMTs and physicians this important cause of hypotension and PDA during ventilation and CPR respectfully. In fact it is critical to include hyperinflation because it likely the most common unrecognized cause of PDA in patients with asthma or advanced COPD.
Upon this realization, a present inventor developed a system and method for teaching healthcare workers to recognize hyperinflation during resuscitation. This system and method is particularly useful when applied with the Bag system disclosed supra. Resuscitation manikins commonly known as “Annie” are in wide use for cardiopulmonary resuscitation (CPR) and advanced cardiac life support training. These devices have a simulated pharynx and trachea, which connects with bilateral airways, which extend to two inflatable elastic bags which simulate the lungs. With the conventional Annie, these airways and trachea are wide open such that the “lungs” deflate at a relatively rapid rate so that the condition of expiratory obstruction is not simulated. The user, often learning how to manually ventilate a patient for the first time, can develop a false sense of the speed of exhalation and is not provided with any simulation which approximates the high risk and often fatal state of airway obstruction and hyperinflation associated with asthma (especially pediatric asthma). They become comfortable with bagging at conventional rates not recognizing the sever risk of hyperinflation in certain patient subgroups. Conventional Annie therefore may actually mislead these healthcare workers into a false understanding of the real complex physiology of bagging during resuscitation. In particular, with pediatric asthma it is easy to over inflate the smaller lungs so these patients are at grave risk so that the false sense of free exhalation provided by Annie is a dangerous deficiency. Indeed death from pediatric asthma and adult asthma after incubation is quite high and this would other wise seem surprising since asthma itself is generally a reversible disease.
According to the present invention a means for inducing airflow restriction and particularly expiratory airflow restriction is applied to at least a portion of the flow path intermediate the resuscitation bag and the “lungs” of the resuscitation manikin to reduce at least the rate of exhalation such that the rate of deflation at least one of the “lungs” is decreased to simulate resuscitation of a patient with asthma or advanced COPD. A fixed restrictor, or a restrictor which provides a variable and selectable degree of restriction to flow within the flow channel, can provide the flow restriction. The flow restrictor can be provided with along the tubing of the resuscitation bag intermediate the bag and the endotracheal tube-connecting member as a fixed member, or can be an accessory which is selectively engaged or attached with the flow path when simulation of airway obstruction is desired. In one embodiment the flow path along or adjacent the endotracheal tube can be provided with a flow restrictor. In the presently preferred embodiment the flow restrictor is provided along or adjacent at least one of the airways and preferably selectably restricts flow along one or both airways between one or both lungs and the resuscitation bag and is preferably hidden from the operators view so that the presence of airflow restriction The flow restrictor can be a provided by providing small diameter trachea and/or airways along their entire length, a region of narrowing in the diameter of the trachea and/or airways, and/or by providing an obstructing member such as a valve within or along the airway, which can be more restrictive during inhalation than exhalation. In one presently preferred embodiment the narrowing is constructed to dynamically enlarge during inspiration and reduce in size during exhalation. A fixed restrictor or a restrictor, which provides a variable and selectable degree of restriction to flow within the flow channel, can provide the flow restriction. In one embodiment the flow restrictor is at least one elastic ring, which compresses a segment of the flow channel. In another embodiment the restrictor is a fixed narrowing of a segment of the flow channel.
The provision of a manikin simulating the physiology of asthma with basic elastic or inelastic airway narrowing (as by the of a simple inelastic ring or elastic ring inserted in, mounted with and/or integral with the airflow path. Both narrow elastic airways, or a fixed narrowing or valve within the airways has the advantages of simplicity and low cost. For example, one low cost embodiment includes an elastic ring (such as a thin wall elastic silicone, poly-isoprene or latex rubber band ring of approximately 2-4 cm in width having a internal diameter in its resting state less than that of the airway) mounted along the airway. The band is mounted so that it can be selectively movable along the airway from a first position wherein the ring is mounted over rigid portion of the airway (so that no airway narrowing or restriction to airflow is provided) to a second position along a compressible portion which is compressed by the elastic force of the ring to narrow the compressible portion and provide elastic flow restriction which is greater during exhalation (when the internal pressure within the airway to elastically distend the ring is less) than during resuscitation bag or ventilator generated inspiration, when the internal airway pressure to distend the ring is greater).
In one the presently preferred embodiment the airflow restrictor is a balloon, which provides variable compression to at least a segment along the flow channel. Preferably two elastic balloons are provided, such as thin walled silicone balloons, each containing a soft collapsible segment of an airway. The balloons are selectively each connected to a separate air vent (which can for example be a pilot tube of the type used for endotracheal tube or tracheotomy tube cuffs). The air vents preferably are connected with a valve (which can for, example, be a syringe the type of valve activated by a luer tip of a syringe as are widely used with the pilot tubes of endotracheal tubes), the tube is further connectable and/or connected with a pump which can be used to selectively inflate the balloon (such as a syringe or, in another example, the hand bulb pump (with a valve) of the type commonly used for blood pressure cuffs). The valve, preferably selectively allows air to escape from the balloons after inflation but which can be closed to allow prolonged inflation as during manikin training sessions, which the present inventor calls “advanced ventilation life support” (AVLS) teaching adult and pediatric asthma resuscitation and ventilation. The pilot tube or vent can be a single tube which bifurcates containing at least one valve between the air vents and the pump so that the pump can selectively inflate one or both balloons to provide selective flow restriction to one or both airways. In another embodiment each vent is connectable with a separate or removable pump (such as a syringes). In one embodiment each with different pressure gauges so that each balloon can be readily inflated to the same or different pressures. In a further embodiment the lungs of the manikin are modified to simulate the effect of loss of elastic recoil of the lungs on the development of dynamic hyperinflation (air trapping) during CPR. An accessory set of replacement lungs with a low elasticity recoil (“emphysema lungs”) is provided which can be applied to replace the more elastic lungs. This modification provides for the opportunity for teaching and improved recognition of the significance of expiratory time when ventilating patients with advance emphysema especially when combined with airway narrowing.
It is the purpose of the present invention to provide a portable manual bag for patient ventilations (and especially emergency ventilation in the field), which provides an indicator of air trapping during ventilation so that children and adults with asthma and/or advanced chronic obstructive lung disease (COPD) have a better chance of survival during resuscitation and ventilation.
It is further the purpose of this invention to provide a resuscitation manikin for advanced cardiopulmonary resuscitation training, which has a means to simulate the pathophysiology of asthma, emphysema, and airway narrowing (including elastic airway narrowing) so that healthcare workers can recognize air trapping during CPR to improve survivability of this group of patients.
It is further the purpose of the present invention to provide a resuscitation bag with an indicator of air trapping in combination with a resuscitation-training manikin having at least heightened airway resistance such that air trapping occurs during normal CPR rates of ventilation so that health care workers can learn to recognize air trapping during routine CPR training.